In addition to the further quotes posted above...
"Please ask yourself this: do you (1) really think that the SETI Institute would issue some sort of major announcement i.e. detection of a signal from another civilization - a week ahead of announcing it formally - and then (2) expect the media to sit on such amazing news - for an entire week? The next time y'all start to whip up a frenzy - out of thin air - use a little common sense before you hit [send]."
From the Search for Extraterrestrial Trailerparks Institute.
Actually at the time of the original posting all it said was a Major Announcement for tommorow. Nothing about a embargo.